1. Field of the Invention
The present invention relates to a process for production of hydrocracked lubricating oil base stocks.
Hydrocracked lube oil base stocks are useful as economical substitutes for stocks which have heretofore been prepared by distillation of crude oils. One of the major drawbacks in using hydrocracked heavy gas oils and solvent-deasphalted oils to manufacture lube stocks is the wide variance in viscosity index of the various lube oil fractions. Typically, viscosity indices of the light neutrals are lower than the viscosity indices of the heavy neutrals and bright stocks. Separate hydrocracking for the heavy and light portions of the feed has been suggested. This procedure is expensive and leads to rapid and serious catalyst fouling.
The process of the present invention reduces the spread of viscosity indices with a simpler and more economical processing scheme than available in prior art, along with reduced catalyst fouling.
2. Description of the Prior Art
U.S. Pat. No. 3,579,435 describes hydrocracking lubricating oil stocks to provide lubricating oils of higher viscosity index by fractionating portions of crude oil suitable for hydrocracking and more severely hydrocracking the higher-boiling fractions by providing additional cracking contacting for the higher-boiling materials.
British Pat. No. 1,233,973 teaches production of lube oil by hydrogenating an organic feedstock with a catalyst having a not-strongly-acidic support, followed by treating the intermediate product with a catalyst having a more strongly acidic support. U.S. Pat. No. 3,242,068 teaches preparation of a lube oil by hydrofining a predominantly paraffinic hydrocarbon oil feed, followed by hydrocracking and isomerizing the hydrofined hydrocarbon feed over a nickel-sulfide-containing or cobalt-sulfide-containing catalyst.
U.S. Pat. Nos. 3,308,055 and 3,663,423 teach hydrocracking processes for producing lubricating oils. U.S. Pat. Nos. 3,240,694, 3,243,367, 3,267,021 and 3,617,482 teach split feed hydrocracking processes for preparing a variety of products. U.S. Pat. No. 3,617,482 is directed to lube oil production.
U.S. Pat. Nos. 3,682,813, 3,617,482, 3,617,484, 3,649,518, 3,649,519 and 3,654,133 teach multiple-stage hydrocracking processes for producing lubricating oils. U.S Pat. No. 3,617,484, in particular, teaches a process for increasing the viscosity index of a light lube fraction, approximating the viscosity range of a 100 neutral oil which has been hydrocracked as part of a relatively wide range fraction, wherein the light lube fraction is isolated and rehydrocracked in the absence of heavier fractions.